During the past year we have completed five studies. Three are on the effects of monocular eyelid suturing on the receptive field development of neurons in the striate cortex, superior colliculus and lateral geniculate nucleus of neonatal rabbits. Such visual deprivation caused a decrease of neurons with oriented receptive fields in the first two structures and an increase of non-responsive and indefinite cells in the lateral geniculate nucleus. The fourth study is an anatomical analysis of the fiber connections of the superior colliculus and lateral geniculate nucleus. The fifth reports a microelectrode investigation of functional subdivisions of the rabbit striate cortex. Current studies include three anatomical investigations: 1) horseradish peroxidase labelling method was used to examine the development of callosal connections of the striate cortex in neonatal rabbits; 2) autoradiographic method was used to trace the retinal fiber distribution to subcortical visual centers and to striate cortex; 3) using specially fixed and 1 micron sections, the existence of laminar body in the rabbit lateral geniculate cells was examined. A study on the long-term visual deprivation effects on neurons in the striate cortex and superior colliculus was continued. This study entailed keeping rabbits with one eye sutured from before eye-opening to at least three years old (rabbit has a normal life span of about five years). Studies to determine the proportions of X- and Y-cells in the lateral geniculate nucleus of both adult and neonatal rabbits were continued.